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1. Field of the Invention
This invention relates generally to the field of wireless communications. More particularly, this invention makes use of and includes multiple antennas attached to an elevating device, such as a crane or cherry picker, and is useful for simultaneously evaluating wireless field strengths at multiple elevations and for locating potential base station sites.
2. Description of the Related Art
Wireless communication has experienced explosive growth. In just a few years cellular telephone usage has soared, and more growth is planned as wireless Internet access improves. This explosive growth has revolutionized data and voice communication.
This explosive growth, however, presents a challenge for wireless service providers. As cellular communication soars in use, more cellular base stations are required. These base stations house equipment for transmitting, receiving, and processing wireless communications to a communications network. Each base station covers a geographic sector, or xe2x80x9ccell,xe2x80x9d and each cell varies in size depending upon the terrain and the number of users. As use of wireless services grows, more cells are needed and, hence, more base stations are required.
Choosing the location for a new base station, however, is extremely complicated. The location of the base station largely determines the quality and range of the cell""s signal coverage. The location of the base station is important because radio waves propagate according to natural laws and not city boundaries. See NEIL J. BOUCHER, THE CELLULAR RADIO HANDBOOK 42 (1995). The tall buildings of urban areas, for example, can both confine radio waves and also cause reflections. See id. at 44. Thus the final location of a base station is often a process of evaluating many potential sites and choosing the location that offers the best compromise of many considerations. See PAUL BEDELL, CELLULAR/PCS MANAGEMENT 24-27 (1999).
Often these potential base station sites are located atop urban buildings or radio towers. Engineers must somehow evaluate the quality and range of a base station signal transmitted from atop a selection of potential buildings or towers. As most cellular designers recognize, the most reliable field strength measurements are obtained when signals are broadcast from the actual site itself (e.g., the roof of the desired building). The field strength could be estimated using mathematical formulae, but these formulae require several correction factors. See BOUCHER, supra, at 59. An actual transmission from or near the potential site, called a xe2x80x9csurvey,xe2x80x9d is therefore necessary to accurately evaluate cellular transmission and reception.
A method of evaluating the communication paths of an elevated antenna uses a crane or cherry-picker. The conventional method involves bringing a large crane or cherry-picker to the potential base station site, and hoisting a boom with an attached antenna to a selected elevation. A transmission is made from the antenna at that elevation, and the field strength of the transmission is measured at various points within the potential cell. Measuring the field strength of the transmission at various points is often referred to as xe2x80x9cdrivingxe2x80x9d a test. Typically, it takes several hours to set up for a test and three hours to drive a test. When all the measurements at a selected elevation are complete, the boom repositions the antenna to next elevation and begins to drive a new transmission to evaluate the field strength at that elevation. For example, an antenna is positioned at 100 feet to drive a first test and then is repositioned at 150 feet to drive a second test.
Cranes and cherry-pickers are very expensive to operate. Because this heavy equipment must often be rented from an independent operator, the rental charges cost hundreds of dollars per hour. Cranes and cherry-pickers, in fact, have been said to unnecessarily double the cost of any survey. See BOUCHER, supra, at 87. Typically, there are multiple elevations to test the field strengths of the transmission paths. Because cranes and cherry-pickers are cumbersome and because of the time involved in setting up and driving a test, only a few elevations, at most, can be evaluated in a work day. One location, in fact, may require two or more work days before moving to the next location. This cumbersome conventional method makes the cell site survey very inefficient.
There is, accordingly, a need for a method and system to simultaneously test multiple transmission paths at different selected elevations in order to accurately measure field strengths at each selected elevation. Further, the method and system must be very easy to install and implement, promote efficient field strength testing, and be cost effective.
The aforementioned problems are minimized by using multiple antennas selectively attached to an elevating device, such as a crane or cherry picker, for testing and locating wireless communications equipment. This invention allows wireless service providers to simultaneously evaluate the field strengths of wireless transmission paths at multiple elevations of potential base station sites. The multiple antenna test system and method make use of a transmitter(s) that is powered by a generator. The transmitter(s) produces test propagation signals that are then selectively broadcast from each of the test antennas. Each test antenna transmits on a unique channel in order to differentiate the elevation of each antenna. For example, an antenna at 150 feet might transmit at 500 MHz, a second antenna at 125 feet might transmit at 666 MHz, and a third antenna at 100 feet might transmit at 717 MHz. Using this invention, multiple elevations of a potential site are typically driven in one survey.
Each test antenna is securely attached to the elevating device at a substantially similar elevation as a proposed siting for a wireless communications antenna. Those skilled in the art will recognize various methods and systems of attaching each test antenna of the elevating device. For example, each antenna could be affixed and mounted on selected locations of the actual boom of a crane. The boom itself would then be raised and/or lowered to fine tune the elevations of the antennas. Alternatively, each antenna could be housed in a protective carrier that is secured to the boom of a crane by one or more connected cables. The cable(s) would connect the protective carrier to a hoisting system. Once the boom has been extended to its maximum height, the hoisting system(s) would fine tune the elevation of each antenna.
The multiple antenna test broadcasts various test propagation signals associated with each antenna. Network interface equipment may be used to process the multiple sets of test propagation signals transmitted from each of the antennas to the multiple receiving locations within the potential cell. The test propagation signals may include the Industrial, Scientific, and Medical (ISM) Band frequencies, such as, 2.4-2.5 GHz, cellular telephone frequencies, such as, 806-960 MHz, 1710-1855 MHz, and 2500-2690 MHz, paging frequencies, digital processing frequencies, and any other frequency in the electromagnetic spectrum. In addition, the type of antenna used to transmit the test signals may be directional or omni-directional.
The multiple antenna test is significantly less expensive than the conventional method. Because the multiple antenna test simultaneously evaluates multiple elevations of a potential site, the costly rental expenses of conventional method are decreased by 50% or more when there are multiple elevations to test at a potential site. In addition, the multiple antenna test also yields more efficient testing. Again, because the multiple antenna test evaluates multiple elevations of a potential site, cellular designers can conduct more tests in a work day. In general, the multiple antenna test can reduce manpower costs by 50% or more when there are multiple elevations to test at a potential site. The multiple antenna test thus promotes more efficient testing, and the total time to complete a survey is substantially reduced.